Currently, to use a manual-approval promotion step, you have to go to the promotion status page for the specific build you want to promote and click the button. It would be nice if this were available from the pipeline view.

The alternative is I think to have the promotion occur automatically if the downstream build is successful, and specify the 'build other projects (manual step)' post-build action. This seems more complicated than just offering a promote capability in the pipeline view itself.